Hell, all of his songs have changed me in some form or fashion but if I really must name one...I'll have to go with...

Free

Dont sleep til the sunrise, listen 2 the falling rain
Dont worry bout tomorrow, dont worry bout your pain
Dont cry unless youre happy, dont smile unless youre blue
Never let that lonely monster take control of u

Be glad that u r free
Free 2 change your mind
Free 2 go most anywhere, anytime
Be glad that u r free
Theres many a man whos not
Be glad 4 what u had baby, what youve got
Be glad 4 what youve got

I know (my? ) heart is beating, my drummer tells me so
If u take your life 4 granted, your beating heart will go
So dont sleep until youre guilty, cuz sinners all r we
Theres others doing far worse than us, so be glad that u r free

Be glad that u r free
Free 2 change your mind
Free 2 go most anywhere, anytime
Be glad that u r free
Theres many a man whos not
Be glad 4 what u had baby, what youve got
Be glad 4 what youve got

Soldiers are a marching, theyre writing brand new laws
Will we all fight together 4 the most important cause?
Will we all fight 4 the right 2 be free?
Free (be glad that u r free)
Free 2 change my mind (free 2 change your mind)
Free 2 go most anywhere, anytime (free 2 go most anywhere,anytime)
Im just glad, Im just glad Im free, yeah (be glad that u r free)
Theres many a man whos not (theres many a man whos not)
Glad 4 what I had baby, (be glad 4 what u had and)
Glad 4 what I got, oh yeah (for what youve got)
Oh Im just glad, Im just glad Im free,yeah (be glad that u r free)
Free 2 change my mind (free 2 change your mind)
Free 2 go most anywhere, anytime (free 2 go most anywhere,anytime)
(be glad that u r free)
(theres many a man whos not)
Im so... (be glad 4 what u had and for)
(what youve got)

Those lyrics, right there, man. Those lyrics have stayed with me always! Those lyrics have saved my life and the lives of many who just don't know how damn glad they should be that Prince's music was in my life, many times!

that was the one

Musicology, that's when I got my tatoo and promised God that I would love him till I die!

2 many to name just one. Always denpends on the mood or circumstance but good post and thread

Last December